The present invention is related to apparatus for protecting oil and gas production tubing passing through a producing zone subjected to the erosive effects of high velocity fluids and solid particles entrained in the fluids flowing into a bore hole around the tubing. More particularly, this invention relates to blast joints to provide maximum erosion protection for production tubing along perforated blast zones providing protection for any length of production tubing including single joints and tubing comprising multiple tubing joints.
It is common when drilling oil and gas wells to encounter two or more producing formations or zones. In such a situation, each producing formation is produced through a separate string of production tubing extending into the well bore. Typically, a string of production tubing extends to the lowermost producing formation. A packer is set about the production tubing string between the producing formations to isolate the upper producing formation from the lower producing formation. A second string of production tubing extends into the well bore to the upper producing formation. A packer is set above the upper producing formation to close off the annulus about the two strings of production tubing so that the upper production zone is isolated between the two packers. Thus, each string of production tubing is in fluid communication with the producing formation adjacent the lower open end of the production tubing. This is commonly referred to as a dual completion well.
Downhole well equipment is exposed to erosive elements in the well bore. This is particularly true in a dual completion well where one string of production tubing extends through an upper producing zone. Flow into the well bore in the upper producing zone, particularly in formations producing high pressure gas, is at high velocities. Abrasive materials, such as unconsolidated sand grains, are often entrained in the fluid stream and impinge on the production tubing. This action is extremely abrasive and erodes the pipe surface, thus requiring replacement of the production tubing. This is a very time consuming process which may be repeated often, particularly for wells having high sand content.
Blast joints adaptable to protecting a series of tubing joints or pipe are disclosed in U.S. Pat. No. 4,685,518, issued Aug. 11, 1987, U.S. Pat. No. 4,726,423, issued Feb. 23, 1988, and U.S. Pat. No. 4,889,185, issued Dec. 26, 1989. While the blast joint assemblies disclosed in such patents are suitable for the intended purposes, field experiences with such blast joints reveal the need for improvements which are met by the present invention. The patented blast joints include erosion resistant rings mounted on tubing sections connectable into production tubing at locations to position the erosion resistant rings along production zones to protect the tubing from erosive materials entering the well bore from the producing zones. The above noted prior art patented devices include coil springs mounted on the tubing joints arranged in spaced relation along the tubing between groups of the erosion resistant rings. The coil springs are compressed sufficiently to urge the erosion resistant rings together in end-to-end array along the tubing. Field experiences have demonstrated several disadvantages in the use of the coil springs to produce the necessary forces for holding the erosion resistant rings together during the handling and installation of the blast joints in a well. The protective rings employed to protect production tubing against high velocity particles are generally tungsten-carbide rings which are held together on the tubing by the coil springs with sufficient compressive force to maintain a continuous sheath of the rings along the tubing while allowing some movement of the rings during the handling of the blast joints required by the installation and operational procedures. During the lifting of assembled blast joints from horizontal positions to the vertical positions necessary to install the joints in a well, the bending stresses are maximum when the joints are in the horizontal position. Tubing joints and blast-ring assemblies are generally hoisted by one end from a horizontal position in the storage rack to a vertical position for installation. During the deflection caused by the horizontal loads on the joints, upper portions of the rings go into compression while lower portions go into tension. The use of the coil springs permits movement of the rings on the tubing to minimize the effects of the forces on the rings caused by the handling. It has been found, however, that the coil springs tend to permit excessive movements of the rings which may damage the rings. During the lowering of the prior art blast joints utilizing coil springs, the rings may rub along the bore hole walls compressing the coil spring and causing the rings to separate which may damage the rings and permit debris to enter the gaps between the rings. Additionally, debris may collect around the coil springs interfering with the ability of the springs to function properly. Further, during installation it may be necessary to jar the tubing string including the blast joint resulting in the rings separating and then the gap between the rings reclosing causing the rings to be chipped.